This invention relates to an inspection method and device for an aperture in a focused ion beam generating apparatus and, more particularly, to a method and device for measuring a diameter of a limiting aperture which limit an ion beam passing therethrough.
A focused ion beam generating apparatus, which generates and irradiates an ion beam focused, is widely utilized in semiconductor lithographic processes such as drawing or modifying patterns on a semiconductor wafer or a photo mask. By scanning an ion beam, it is possible to produce an opaque material to modify a white defect, though it is also possible to remove an opaque material to modify a black defect. Nowadays it is required to control an focused ion beam with accuracy of an order of sub-microns in dimension in order to draw or modify a pattern on a photo mask applied to integrated circuits. Therefore the apparatus should be regularly inspected so as to operate with desired accuracy.
Accuracy in dimension of an ion beam mostly depends on dimension of a limiting aperture. The limiting aperture is formed on a limiting aperture plate which has a function to limit an ion beam passing therethrough within a desired diameter. Therefore, a peripheral part of the aperture on the plate always suffers from spattering with ion beam so that a diameter of the aperture becomes larger and larger as time passes. With the above described reason, it is very important to regularly inspect or measure a diameter of the limiting aperture and confirm that the measured diameter is in a proper range to ensure the operation of the apparatus with desired accuracy.
However, in a conventional inspection method for a limiting aperture, much labor is required. That is, an inspector has to remove the limiting aperture plate from the apparatus, measure a diameter of the aperture on the plate and assemble it into the apparatus again. Removing the aperture plate is not an efficient work for regular inspection.